On preferred Mn site in multiferroic BiFeO3: A view by synchrotron x-ray absorption near edge structure spectroscopy

Synchrotron X-ray Near Edge Structure (XANES) experiments were performed on Mn-doped BiFeO3 samples and compared with ab initio XANES calculations. The Fe and Mn K-edge XANES measurements were carried out on Mn-doped BiFeO3 powders (with 5-40 Mn mole%). Both XANES spectra were obtained in a fluorescent mode at ambient temperature with a Ge(111) double crystal monochromator. From the XANES results, it was clearly identified that the oxidation state of both Fe and Mn ions in BiFeO3 structure was +3. The features of the measured Mn K-edge XANES were consistent with ab initio XANES of Mn on the Fe site and inconsistent with Mn on other sites. The clear agreement between measured and ab initio theoretical XANES spectra was the strongest evidence of Mn substituting for Fe in BiFeO3 structure for low Mn content. More interestingly, at higher Mn content, the presence of a second phase precipitation of BiMnO3 and BiMn2O5 was evident. This clearly indicated the Mn solubility limit in the BiFeO3 structure, while the two trace compounds could also be responsible for the relevant properties reported in Mn-doped BiFeO3 materials. (C) 2014 AIP Publishing LLC.